If they are "falling apart" over this on a 4 hour flight, perhaps they ought not to travel alone. What are they going to do if something horrific such as a misconnect or a delayed bag occurs? Seriously, they need to put this in perspective.

DL agents have clear instructions on BE and DL audits changes for this reason. They are free to call, but this isn't one of those things where a kindly agent can do what they want by keying in a couple of sequences.

Their best bet is not to check-in and to handle seats at the gate. While the likelihood is that they both wind up in lousy middle seats, if they don't have seat assignments, the GA must address the issue and to the extent that there are seats close by (bear in mind that across aisles or one behind the other ought to be manageable without "falling apart"), that is where a decent GA can be helpful. Once you've got auto-assigned seat assignments, even GA's have to do extra work to move a BE pax.